Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

Influence of electroosmotic treatment on the hydro-mechanical behaviour of clayey silts: preliminary experimental results

Preliminary results of an investigation focused on the influence of electrokinetic treatment on the mechanical and hydraulic behaviour of clayey soils are presented. The experimental programme aims at providing a contribution to the sustainability of contaminant extraction or containment via electroosmosis. Changes in the hydraulic and mechanical properties of two illitic clayey soils, subjected to a DC electric field, were investigated. Samples of the two soils were subjected to electrokinetic filtration, for different periods of time, and under different constant loads. Afterwards, they were tested under one-dimensional compression to detect changes in stiffness and hydraulic conductivity due to the electrical treatment. After the application of a DC field for a few hours, a small reversible increment in the average soil stiffness was observed, with respect to the untreated soil, while the hydraulic conductivity was not affected substantially. Dramatic changes of the mechanical and hydraulic soil properties, correlated to changes of the soil pH, were observed following non-conditioned electrokinetic treatment with duration of the order of days.     

Modelling of catalyst pellet poisoning for benzene hydrogenation

Based on the kinetics of benzene hydrogenation, pore diffusion and catalyst deactivation, time-dependent effectiveness behaviour of a single Ni? SiO₂? Al₂O₃ catalyst pellet where the chemical reaction rate is determined by pore diffusion was simulated for different conditions of operation. Poisoning kinetics were measured in a series of differential reactor experiments at atmospheric total pressure at temperatures ranging from 403 to 473 K. A computed effectiveness factor has been compared with experimental values for a catalyst pellet of industrial size. A good degree of correlation between theoretical prediction and the experimental results was found.     

Chemical vapour infiltration and mechanical properties of carbon open-cell foams

In order to improve their mechanical properties, carbon open-cell foams of two different pore sizes were infiltrated with pyrocarbon by chemical vapour deposition at reduced pressure and using pure propane as precursor. The optimal conditions in terms of deposition rate and uniformity in coating thickness, structure and anisotropy were first investigated. Foam specimens were infiltrated at various stages, with two pyrocarbons of distinct microtextures and their morphology, relative density and geometrical features were evaluated.Compressive crushing tests were conducted to determine the influence of the pore size, the pyrocarbon type and the relative density on the mechanical properties of the pyrocarbon-infiltrated foams. They retain their non-brittle and dissipating behaviour up to relative densities of 0.15. The stiffness, crushing strength and dissipated energy increase significantly with the relative density. The crushing behaviour of the pyrocarbon-foam specimens can be essentially explained using simple structural models and failure mechanisms, according to the Gibson & Ashby’s approach for brittle cellular solids.     

Lipid soil removal from cotton fabric after mercerization and carboxymethylation finishing

Soiling and soil removal from cotton fabrics that had been chemically modified by mercerization and carboxymethylation were studied using electron microscopy and radiotracer techniques. The distribution of lard soil in specimens before and after laudering was determined by means of chemical tagging with osmium tetroxide. Both the chemical and physical changes of the cotton resulted in differences in soiling and soil removal of lipid soil. Mercerization and carboxymethylation of cotton swell the cotton fiber, decrease the crenulation and the lumen, and smooth the fiber surface. These finishes also increase the pore volume and thus the chemical accessibility of the fibrillar structure. In addition, carboxymethylation causes changes in the chemistry of the fiber by increasing the carboxyl group content. These structural changes reduce the amount of soil deposited in the lumen of the fiber, particularly for the carboxymethylated cotton. They also increase soil removal from the crenulation and the interfiber spaces in the yarn bundle. Soil removal from fiber surfaces and from within the fiber—both lumen and secondary wall—was highest for the carboxymethylated cotton, and mercerization also enhanced lipid soil removal. The results of this experiment indicate that chemical accessibility and hydrophilicity of the fiber structure influence both soil deposition and soil removal of lipid soils. Soil removal of these modified cottons is enhanced by multiple mechanisms: (i) the decrease in small crevices and the crenulation or small capillary along the fiber, (ii) the increase in pore volume that enhances chemical accessibility and thus detergency within the fiber structure, (iii) the increase in hydrophilicity that enhances soil removal from the surface by the roll-up mechanism, (iv) the increase of mechanical action due to enhanced swelling of the carboxymethylated cotton, and (v) the reduction of soil redeposition on carboxymethylated surfaces.     

Critical coagulation in sulfidic sediments from an east-coast Australian acid sulfate landscape

Sulfidic clays are agriculturally and environmentally important. In this work we examine the impacts of electrolytes and pH on the behaviour of colloidal clay mineral particles extracted from such sediments. The distribution of ferrous iron released by pyrite oxidation, aluminium by acidic weathering and cations in soils and pore waters in the field are reported. The behaviour of open-structured sulfidic colloidal clay mineral particles in response to changes in solution ionic composition were studied; (i) to evaluate the effects of natural oxidation of iron sulfide material in pedogenic development, and (ii) to investigate the response of these sediments to changes in pore water ionic composition as an option for soft sediment engineered dewatering. Photon correlation spectroscopy (PCS) was used to quantify these effects. As expected, Mg²⁺ and Ca²⁺ were more effective in inducing coagulation of the colloidal clay mineral particles than Na⁺; however, the effect was more pronounced than theoretically expected according to DLVO theory. Comparing the presence/absence of protons in cation saturated experiments showed new evidence for the formation of H-colloidal clay mineral particle complexes that resist competitive cation exchange. The critical concentrations of acidic cations required for mass rapid aggregation in these experiments is comparable to the pore water composition within the soil profile where structural collapse has already occurred.     

A Unified Approach for Predicting the Strength of Cracked and Non-Cracked Adhesive Joints

This paper presents an investigation of suitable failure criteria for predicting the strengths of uncracked and interfacially-cracked adhesively-bonded joints. A detailed experimental study of both bulk adhesive and adhesive joint behaviour has been carried out. The effect of both strain rate and temperature on the response of the adhesive to mechanical loading has been investigated through a series of tensile tests. The resulting data were used to construct an empirical model for the behaviour of the adhesive, A novel test method based on a four-point bend specimen has been used to investigate how the hydrostatic stress affects the response of the adhesive. Extensive tests on adhesive joints, subjected to different modes of loading and different lengths of interfacial cracks, have provided comprehensive joint strength data and insight into the site and locus of joint failure initiation. Following this, various failure criteria have been evaluated by carrying out detailed linear elastic and non-linear elasto-plastic two-dimensional analyses of the joints tested. Three-dimensional analyses provided modified loads for these two-dimensional analyses that more accurately reproduce the conditions on the plane of failure. Criteria based on critical stress or strain components at a distance from the point of singularity were investigated A procedure for accounting for the strain rate effects of the adhesive has been incorporated with the non-linear analyses. Criteria based on critical energy release rates have been evaluated from the linear elastic analyses of the joints with interfacial cracks diminishing to very small sizes. Finally, non-linear springs along a plane of failure have been used to model a line of localised damage, resulting in joint failure criteria based on a critical opening displacement. This last method provides the most physically acceptable way of predicting the strength of cracked and non-cracked joints using the same failure criterion.     

Effects of sample size on capillary pressures in porous media

Capillary pressure curves and their hystereses depend not only upon the geometry and wetting properties of the individual pores of a porous sample, but also upon the accessibility of these pores from the surface of the sample. Dependence of accessibility on distance from the surface of the sample implies that capillary pressure curves are sensitive to sample size. This sensitivity is investigated by measuring capillary pressure curves for porous samples of varying thickness. A theoretical investigation of sample thickness effects is made through application of the concepts of percolation theory of chaotic media. In the theory presented here, functions describing accessibility and pore size distribution appear in integral equations which account for all prominent features of drainage and imhibition, including threshold pressure, hystereses, residual saturations and dependence of residual saturation on initial saturation. The character and magnitude of sample thickness effects predicted by percolation theory are generally consistent with experimental results.     

Liquefaction of saturated loose and cemented granular soils

A coupled continuum-discrete hydromechanical model was utilized to analyze the liquefaction of saturated granular soils in loose and cemented deposits. The pore fluid motion was idealized using averaged Navier-Stokes equations and the discrete element method was employed to model the granular particles. Parallel bonds were used to idealize the effects of inter-particle cementation. Well established semi-empirical relationships were utilized to quantify the fluid-particle interactions. Numerical simulations were conducted to investigate the response of saturated granular deposits when subjected to a dynamic base excitation. The outcome of these simulations was consistent with experimental observations, and revealed a number of salient micro-mechanical mechanisms associated with soil liquefaction and the impact of cementation. The employed continuum-discrete hydromechanical model provides an effective tool to assess the intricate micro-mechanical response mechanism of saturated loose and cemented soils.     

Development of a detailed kinetic model for gasoline surrogate fuels

A detailed chemical kinetic model to describe the autoignition of gasoline surrogate fuels is presented consisting of the fuels iso-octane, n-heptane, toluene, diisobutylene and ethanol. Model predictions have been compared with shock tube ignition delay time data for surrogates of gasoline over practical ranges of temperature and pressure, and the model has been found to be sensitive to both changes in temperature and pressure. Moreover, the model can qualitatively predict the observed synergistic and antagonistic non-linear blending behaviour in motor octane number (MON) for different combinations of primary reference fuels (PRFs) and non-PRFs by correlating calculated autoignition delay times from peak pressures and temperatures in the MON test to experimental MON values. The reasons for the blending behaviour are interpreted in terms autoignition chemistry.     

Oxidative functionalization of carbon nanotubes in atmospheric pressure filamentary dielectric barrier discharge (APDBD)

The surface compositional and any structural changes that occur on carbon nanotubes using air-atmospheric pressure dielectric barrier discharge (APDBD) for functionalization are investigated employing Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and neutron diffraction techniques. Atmospheric pressure plasmas (APP) are suggested to be particularly suitable for functionalization of aligned nanotubes, where wet chemical manipulation could damage or even destroy the highly desirable vertical alignment. In this work a detailed experimental study elucidating the effects of APDBD plasma treatment parameters (e.g. power density, discharge composition, inter-electrode gap and treatment time) on the electronic structure, physical, and chemical behaviour of carbon nanotubes has been conducted. In an atmospheric air we find an optimal oxidative functionalization of CNTs in our DBD system within few seconds (<5 s) at a discharge power of ∼0.5 kW. This investigation may find useful application as functionalization technique for CNT engineered devices and sensors.     

On the onset of current oscillations at the limiting current region emerged during iron electrodissolution in sulfuric acid solutions

The onset of current oscillations emerged at the limiting current region (LCR) during iron electrodissolution in sulfuric acid solutions is investigated in this work by using a number of perturbation experiments. Perturbation experiments on the Fe|n M H₂SO₄ system were conducted through the: (a) insertion of a series external resistance, (b) rotation of the Fe-disc electrode, (c) injection of various chemical species on the Fe surface and (d) change of the position of the Fe electrode. Electrical, mass-transport and chemical effects, all were found to influence the onset of current oscillations. These effects were combined with previously developed ideas concerning the formation of a ferrous salt layer along with the partial passivation of the Fe electrode. A plausible mechanism is proposed, able to explain the onset of current oscillations at the beginning of the mass-transfer controlled LCR. This mechanism agrees with experimental observations and may explain: (i) why current oscillations emerge within a fixed potential region at the LCR, (ii) why the IR-drop along with appropriate hydrodynamic conditions are both required for the onset of oscillations and (iii) what is the role of hydrodynamic conditions and chemical composition of the layer formed at the LCR.     

三种VOCs物性对其在活性炭上吸附行为的影响

为了探讨VOC物性对活性炭吸附行为的影响,对活性炭表面物化性质进行了表征.并以甲苯、丙酮、二甲苯为吸附质,在同等实验条件下进行了固定床吸附实验.实验结果显示活性炭对3种VOCs的吸附量为二甲苯＞甲苯＞丙酮.将实验结果与VOC物性进行关联分析,结果表明:活性炭对有机气体的吸附量随着吸附质的分子量、分子动力学直径、沸点、密...     

Simulation of catalytic fluidized bed reactors by a transient axial dispersion model with invariant physical properties and nonlinear chemical reactions

This paper presents a transient axial dispersion model for an isothermal, catalytic fluidized bed reactor, which is frequently employed in synthetic production processes including coal gasification and liquefaction. A non-linear chemical reaction is considered to occur in the reactor. This model of a fluidized bed reactor takes into account the axial dispersion in the three phases, bubble, cloud-wake and emulsion. The physical properties along the axial coordinate are invariant in the model. Transient characteristics of the gas reactant, and the length of the transient period have been examined based on the model. The model compares favorably with experimental data in the steady state condition.     

不同方法测定水泥土渗透系数的研究

为研究适合测定水泥土渗透系数的试验方法,结合工程实际,对防渗墙进行现场钻孔注水试验,对钻芯取样的水泥土试样进行室内变水头渗透试验和三轴渗透试验,对比室内试验结果和现场试验结果,探讨适合检测水泥土芯样的室内试验方法,分析三轴渗透试验中孔隙水压和围压对水泥土渗透性的影响。对重新配制的水泥土试样进行室内变水头渗透试验、三轴渗透试验及水泥土渗透试验,研究不同方法测定水泥土渗透系数的差异。试验结果表明:三轴渗透试验比室内变水头渗透试验更适合测定水泥土芯样渗透系数;三轴渗透试验中,围压为0时,水泥土芯样渗透系数会随着孔隙水压的增加而增加,围压改变时,会随着围压的增加而减小;三种室内渗透试验方法测定水泥土试样的渗透系数基本相接近,都可用于测定水泥土试样渗透系数。     

Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.     

Membrane Characterization Based on PEG Rejection and CFD Analysis

Characterization of membrane pore size by experimental methods is usually done by the determination of the rejection of polymeric molecules having a range of sizes such as PEG. These experiments are affected by concentration polarization, which can lead to erroneous interpretation of the results, mainly because the concentration and the permeate flux change along the membrane surface. Additionally, experimental methods alone are insufficient to obtain the membrane pore size. To improve the current approach, numerical methods are used to understand mass transport limitations in rejection experiments and to predict the membrane pore size. In the current study, the results show that the ultrafiltration membrane has a MWCO of 20 kDa, different from the value set by the manufacturer (30 kDa). For the experimental conditions, concentration dependent viscosity and osmotic pressure do not influence the permeate flow rate or rejection. Moreover, the membrane pore size was found to be 2.59 nm. This value was determined comparing rejection values obtained by numerical and experimental results. Numerical analysis is also important to characterize the flow and mass transport in each point at membrane surface.     

Mechanical/thermal dewatering of lignite. Part 3: Physical properties and pore structure of MTE product coals

The mechanical thermal dewatering (MTE) process has been shown to effectively dewater high moisture content low rank coals via the application of mechanical force at elevated temperatures.Using mercury intrusion porosimetry (MIP) as an investigative tool, this study examines how MTE processing conditions, such as temperature and pressure, affect the compressibility, pore size distribution, apparent (skeletal) density and shrinkage behaviour of three low rank coals sourced from Australia, Greece and Germany. As both pore filling and sample compression occurred at high mercury intrusion pressures, all MIP data were corrected for compression effects by using compressibility values derived from mercury extrusion data.The MTE process is shown to produce a low porosity coal, which, depending upon the processing conditions used, undergoes further shrinkage upon oven drying at 105 °C. An increase in MTE temperature (above about 85 °C) led to an increase in mesopore volume, which is caused by a hardening of the coal structure, leading to pore volume retention and a consequent reduction in percent shrinkage on oven drying. The increase in measured mesopore volume is also associated with an increase in measured surface area.The reverse trend is seen with increasing MTE pressure, where both the macro and mesopore volume decrease with pressure, causing the percent shrinkage to increase accordingly. This effect may be due to an increase in capillary forces caused by a decrease in the average pore diameter. The percent shrinkage increased up to a pore volume of about 0.1 cm³/g, beyond which no further reduction in pore volume was achieved. The decrease in mesopore volume is also associated with a decrease in measured surface area.Compressibility values derived from mercury extrusion data show that the MTE process has little impact on the network strength of the skeletal network structure of all three coals investigated. Likewise, the skeletal density remained relatively unchanged.The reduction in water content, pore volume and the changes in shrinkage behaviour under increasingly severe MTE conditions are suggestive of the physical changes that accompany increased coalification (rank) within the lignitic range.     

Electrothermal explosion under pressure: Ti–C blends in porous electroconducting envelope

Influence of applied pressure P and intensity of Joule heating on electrothermal explosion (ETE) in Ti–C blends placed in a porous electroconducting envelope was studied by using a home-made experimental setup. A distinctive feature of this system is non-linear warm-up prior to initiation of ETE. A non-linear temperature growth during pre-explosion warm-up was associated with gradual decrease in the electrical resistance of the sample caused by intensification of mass transfer processes leading to an increase in current density and hence in heating rate. During the warm-up period, the extent of conversion was found to attain a value of about 15%. In classical theory of gasless combustion, chemical reaction within the warm-up zone is neglected and it is postulated that combustion reaction gets started at temperatures close to the melting point of a low-melting reagent. Our results cast some doubt on the validity of the above adoptions and thus shed new light on the mechanism of SHS reactions in heterogeneous systems.     

Time-dependent polarization behaviour of pipeline grade steel in low ionic strength environments

A bench-top experimental approach is described for estimation of the polarization behaviour of pipeline steel as a function of the time-dependent formation of scale and calcareous deposits in simulated soil leachates. A three-time constant process model provided a common set of parameters for a given soil environment and level of aeration. The parameters estimated could be applied to a broad range of current values and were independent of time, potential and applied current. The experimental approach, model and regression procedure are general and could be used to determine the physical parameters associated with the seasonal variations (wet–dry cycles) in the soils surrounding pipelines or with other factors that influence general corrosion. The polarization model could provide a boundary condition for mathematical models for cathodic protection of pipelines or other buried structures. The separation of current contributions implicit in the model can be used to assess the reduction of corrosion current associated with specific CP criteria.